The present invention relates to a device for the production of a reaction mixture, which forms a foamed plastic, from at least two reaction components and a foaming agent.
A device of this kind is distributed by MASCHINENFABRIK HENNECKE GMBH, 30 Birlinghovener Strasse, D-53754 Sankt Augustin, and is described in the company publication "DELTAMAT", No. 48, 3T 08/92 Ha, page 3 in respect of the foaming agent supply.
Low-boiling foaming agents, such as R22 (compare "Kunststoffe" (Synthetic Resins) 80, 1990, Vol. 8, page 909) are being used to an increasing extent to replace foaming agents containing fluorinated hydrocarbons. The foaming agents are supplied in pressure containers of different sizes which can generally be directly coupled to the pipeline system. Mixing with the reaction components, generally with the polyol, is carried out at a pressure of approximately 20 bar, and the mixture is introduced into an intermediate container, in practice referred to as the "working container", and maintained under pressure. Monitoring devices, for example mass flow measuring devices, are used to monitor the precise adherence to the mixing ratio. The mixture produced in this way naturally possesses a lower vapor pressure than the foaming agent by itself; however, due to the pressure prevailing in the intermediate container, the mixture always remains in the liquid state.
If pressure differences occur in the intermediate container, or if air and/or foaming agent gases escape as a result of leaks from the agitator shaft, this can lead to losses of foaming agent from the produced mixture. These losses inevitably give rise to a changed, poorer quality of foamed plastic. Because of the volatility of the foaming agents, it is not possible to determine the foaming agent content under atmospheric conditions.
It is known from U.S. Pat. No. 4,526,907 to supply a recirculation line to the working container and to place in such a line a constant working circulating pump and a device for measuring the gas content.
The object exists of designing a device in such manner that it is possible to determine the current foaming agent content of the mixture continuously and under the pressure conditions prevailing in the intermediate container .